Permanent magnet rotor structure for a dynamoelectric machine



June 25, 1968 EBERUNE ET AL 3,390,291

PERMANENT MAGNET ROTOR STRUCTURE FOR A DYNAMOELECTRIC MACHINE OriginalFiled July 5, 1962 2 Sheets-Sheet 1 United States Patent 3,390,291PERMANENT MAGNET ROTOR STRUCTURE FOR A DYNAMOELECTRIC MACHINE Richard F.Eberline, Rochester, and Thomas F. Carmichael and Edward A. Schilling,Drayton Plains, Mich., assignors, by mesne assignments, to MichiganBank. National Association, a national banking association Originalapplication July 3, 1962, Ser. No. 207,264, now Patent No. 3,368,275,dated Feb. 13, 1968. Divided and this application Sept. 28, 1967, Ser.No. 671,252

Claims. (Cl. 310-156) ABSTRACT OF THE DISCLOSURE A permanent magnetrotor structure for a dynamo electric machine utilizing a separate unitholding a cluster of permanent magnets and a supporting ring forsupporting the separate unit with the supporting ring being apreexisting component serving a function in a machine assembly, otherthan as a part of a generator, in which it is adapted to be rotated.

The present application is a divisional of our copending patentapplication Ser. No. 207,264, filed July 3, 1962, now Patent No.3,368,275, issued Feb. 13, 1968, to Richard F. Eberline et al. forGenerator and Method of Manufacture.

This invention relates to generators, and more particularly to aconstruction for permanent magnet alternators of the type having a rotorring carrying circumferentially spaced permanent magnets .of the ceramictype.

The use of ceramic type permanent magnets for the outside rotors ofpermanent magnet alternators has certain advantages, among which is thefact that a predetermined amount of induction can be obtained withceramic magnets which are shorter in a radial direction as compared withAlnico magnets. However, in order to achieve the desired fluxconcentration, metallic shoes are placed on the inner surfaces of theceramic magnets facing the stator.

It is an object of the present invention to provide a novel and improvedconstruction for permanent magnet alternator rotors in which ceramicmagnets and their associated metallic shoes will be rigidly secured in aunitary arrangement, facilitating their assembly in an outer support,such as a flywheel or ring gear unit.

It is a general object to provide an improved rotor construction for agenerator.

Other objects, features, and advantages of the present invention willbecome apparent from the subsequent description, taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a partly sectioned plan view of the magnet and shoe assemblyafter casting and machining but before it is placed in a ring support;

FIGURE 2 is a cross-sectional view taken along the line 22 of FIGURE 1and showing the assembly mounted in a support ring;

FIGURE 3 is a cross-sectional view taken along the line 3--3 .of FIGURE1 and showing the shape of the casting between magnets;

FIGURE 4 is a partial cross-sectional view in elevation of a suitabledie assembly for molding the magnetsupporting casting, showing themagnets and shoes in position;

FIGURE 5 is a fragmentary plan view of the lower die member, showingmagnet-supporting and positioning elements;

FIGURE 6 is a front view of one of the magnet shoes;

3,390,291 Patented June 25, 1968 FIGURE 7 is a front view of a modifiedform of magnet shoe in which edge portions are crimped around theceramic magnet; and

FIGURE 8 is a cross-sectional fragmentary view taken along the line 88of FIGURE 7 and showing the manner in which the shoe portions engage themagnet.

Briefly, the illustrated embodiment of the invention comprises aplurality of circumferentially spaced curved ceramic magnets, eachhaving a relatively thin metallic shoe engaging its concave surface,with a cast ring of nonmagnetic material engaging and partiallysurrounding the magnets, the ring serving to support the magnets andshoes and permitting them to be assembled as a unit into a supportingring of magnetic material which engages the magnets. One great advantageof the present invention is the use, as noted in the objects, of theunit, i.e., cast ring,

magnets, etc., in combination with a pre-existing component, such as afly-wheel, ring gear, etc., to define the supporting ring of magneticmaterial. Note that the flywheel or the like is a pre-existing componentnormally serving a first function in a machine assembly other than afunction as a portion of a generator and in such first function isadapted to be rotated. Thus the pre-existing component provides therotational force to the generator, provides a magnetic return path forthe magnets, acts as a support for the unit and still performs itsoriginal function i.e. flywheel or gear, etc.

As a suitable process for making the magnet and shoe assembly, amultiple member die or mold is provided, the magnets being positionedtogether with the shoes within the die while in a magnetized condition,the die members being provided with locating and supporting elements forthe magnets and shoes. After the casting is formed the magnets aredemagnetized, after which the unitary magnet and shoe assembly is placedin the supporting ring, the ring being previously heated so that it willshrink into tight engagement with the assembly. The cast ring is thenmachined at room temperature to remove its interior sufficiently toexpose the magnet shoes, and the magnets are then remagnetized.

Referring more particularly to the drawings, FIG- URES 1, 2 and 3 showthe magnet and shoe assembly which is generally indicated at 11 and isintended to be mounted in a supporting ring of magnetic materialgenerally indicated at 12 and shown partially in dot-dash lines inFIGURES 2 and 3 and as previously noted the supporting ring isadvantageously a pre-existing component such as a flywheel, ring gear,etc. In its finished form, assembly 11 comprises a plurality .ofcircumferentially spaced ceramic magnets 13 which may be fabricated byany of several known methods. Each magnet 13 has a concave inner surface14 and a convex outer surface 15, these surfaces being concentric andbeing connected by parallel sides 16. Each magnet is provided with ashoe 17 of magnetic material, the width and length of this shoe beingsubstantially the same as the width and length of magnet surface 14, theshoe having concentric concave and convex surfaces with the convexsurface being complementary to surface 14. The edges 18 of shoes 17 arebeveled as shown in the figures, the bevel being in an inward directionfrom the convex surface to the concave surface.

An annular casting of nonmagnetic material generally indicated at 19holds magnets 13 and shoes 14 together. Cast ring 19 is somewhat widerthan magnets 13, as seen in FIGURE 2. The outer convex surface 21 ofring 19 is on the same diameter as the convex surfaces 15 of magnets 13,that is, surfaces 15 and 21 are flush or contiguous. At the location ofmagnets 13, surface 21 is relatively narrow, as seen in FIGURE 2,Whereas surface 21 is relatively wide between magnets 13, as seen inFIG- URE 3.

The thickness of ring 19 in its final form is equal to the combinedthicknesses of magnets 13 and shoes 17, as seen in FIGURE 2, and thewidth of ring 19 is somewhat greater than the width of magnets 13 andshoes 17. The ring is thus formed with portions 22 and 23 which engagethe axially spaced end surfaces 24 and 25, respectively, of magnets 13and the end bevel edges 18 of shoes 17, portions 22 and 23 of ring 19holding shoes 17 against magnets 13. If ring 19 is fabricated inaccordance with the method to be described below, portions 22 and 23will be partially removed in the areas between magnets, as seen inFIGURE 3. The inner surfaces of portions 22 and 23 adjacent shoes 17will be flush with the inner shoe surfaces, as will be noted in FIGURE2. Portion 23 of ring 19 extends radially outwardly to surface 21,whereas portion 22 extends outwardly a lesser distance, terminating inan inclined or frustoconical surface 26. The axially spaced outersurfaces of ring portions 22 and 23 are parallel to magnet surfaces 24and 25.

FIGURES 4 and illulstrate a mold or die construction for formingassembly 19. The mold or die assembly is generally indicated at 27 andcomprises a lower die member 28, an upper die member 29 and anintermediate die member 31. These die members are suitably fabricated ofmagnetic material such as steel and are of circular shape, member 28having an upwardly facing fiat central surface 32, a flat surface 33outwardly of surface 32 and spaced thereabove, and an outer retainingshoulder 34 for intermediate die member 31. Surfaces 32 and 33 areconnected by an inclined or frustoconical surface 35 which serves toform ring surface 26. A plurality of circumferentially spaced magnet andshoe supporting elements 36 extending upwardly from surface 32immediately inwardly of surface 35. Each element 36 comprises afiat-topped projection extending upwardly somewhat higher than the levelof surface 33 but with a pair of end surfaces 37 which are flush orcontiguous with surface 33 as seen in FIG- URE 5, thus forming verticalshoulders 38. The spacing between shoulders 38 of adjacent elements 36is equal to the length of each magnet 13 in a circumferential directionso that a magnet 13 and a shoe 17 may be retained between each adjacentpair of elements 36, as seen in phantom lines in FIGURE 5.

Upper die member 29 has an inner downwardly facing flat annular surface39 which terminates at a shoulder 41 having the same diameter asshoulder 34. A downward extension 42 is centrally formed within surface39, this extension terminating in a lower flat surface 43 engageablewith surface 32. The total length of extension 42 is such that thedistance between surfaces 32 and 39 will be equal to the desired initialthickness of ring 19; this will be determined by the width of magnets 13and shoes 17 in an axial direction. A plurality of circumferentiallyspaced downward projections 44 are provided on surface 39; theseprojections are shaped similarly to projection 36 so as to be insupporting relation with magnets 13 and shoes 17.

Intermediate die member 31 is of annular shape, having a lower flatsurface 45 engageable with surface 33 of die member 28 and an upper fiatsurface 46 engageable with surface 39 of die member 29. The distancebetween surfaces 45 and 46 will likewise be determined by the width ofmagnets 13 and shoes 17. Outer surface 47 of die member 31 issubstantially the same as the diameter of shoulders 34 and 41, and thethickness of die member 31 is such that its inner surface 48 will be insupporting relation with the outer surfaces of magnets 13. A pluralityof recesses 49 and 51 may be provided in die members 28 and 29,respectively, for separating purposes. It should be noted that thecylindrical surface 52 of extension 42 is spaced inwardly from surface48 a distance such that a space will exist between the concave surfacesof shoes 17 and die surface 52.

In carrying out the novel process of fabricating assembly 11, centraldie member 31 will be mounted on lower die member 28 and magnets 13 intheir magnetized condition, together with shoes 17, will be placed withproper polar orientation between shoulders 38 on lower die member 23,the magnets resting on surfaces 37 of projections 36 and die surface 33,shoes 17 being supported by surfaces 37. Because of the magnetizedcondition of magnets 13, their outer convex surfaces will be held firmlyagainst intermediate die member 31, and their inner concave surfaceswill hold shoes 17. Glue or other adhesive material may be used betweenmagnets 13 and shoes 17 for aiding in retention of the shoes on themagnets. Upper die mem ber 29 will then be mounted on intermediate diemember 31, projections 44 engaging the upper portions of magnets 13 andshoes 17 while surface 43 of upper die member 29 engages surface 32 oflower die member 28.

The molten material which will form ring 19 is then poured or injectedinto the cavity formed by the die members through a suitable gate (notshown). This material may be aluminum, zinc, bismuth or anothernonmagnetic metallic or plastic substance having the desired strengthcharacteristics. Heat from the material forced into the mold will atleast partially demagnetize magnets 31, thus facilitating removal ofassembly 11 from mold 27.

The gate and the sprue formed between surfaces 32 and 43 will then beremoved, the sprue being indicated in dotdash lines at 53 in FIGURE 2.Magnets 13 will then be demagnetized, this being done to facilitate thelater machining step.

Assembly 11 may then be mounted in supporting ring 12. The ring is shownin FIGURE 2 as having an annular surface 54 for supporting assembly 11,this surface terminating in an inwardly extending shoulder 55. Ring 12may be previously heated and assembly 11 slipped into the ring, portion22 first, until it engages shoulder 55; an appropriate lubricatingsubstance may be used for this purpose if desired. As ring 12 cools, itwill shrink into tight engagement with assembly 11, being in directcontact with exposed convex surfaces 15 of magnets 13 to form anefficient flux path.

The assembly comprising unit 11 and ring 12 may then be machined at roomtemperature to remove the excess portions of casting 19. These excessportions are indicated in dot-dash lines at 56in FIGURES 2 and 3 andwill comprise the material radially inwardly of inner shoe surfaces 17and axially outwardly of the end surface 57 of supporting ring 12.Magnets 13 may then be remagnetized to complete the fabrication process.In the case where supporting ring 12 is most advantageously selected tobe a pre-existing component such as a flywheel, ring gear, etc., therotor of the generator is defined by an assembly including a componentwhich is in accordance with its first function adapted to be rotatedwith the component also acting as a support while providing the returnmagnetic path for the magnets 13. Thus with this construction, the needfor a separate drive for the rotor is eliminated.

FIGURES 7 and 8 show a slightly modified form of the magnet shoe, theshoe being indicated generally at 101. Shoe 101 is generally similar toshoe 17, having convex and concave surfaces with the convex surfacecomplementary to the concave surface of magnet 102. However, the outerdimensions of shoe 101 are slightly larger than those of magnet 102, sothat portions 103 of beveled edge 104 may be formed into coined orlanced retention lugs for aiding in the positioning and retention of theshoes on the magnets. Four such portions 103 are shown, one beinglocated at the central portion of each beveled edge. The use of theselugs may eliminate the need for glue or other adhesive substance duringthe assembly process, and portions 103 will also coact with the castmaterial to enhance the rigidity of the assembly.

While it will be apparent that the preferred embodiments of theinvention disclosed are well calculated to fulfill the objects abovestated, it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the properscope or fair meaning of the subjoined claims.

What is claimed is:

1. In a dynamoelectric machine, a permanent magnet rotor constructioncomprising an annular separate unit having a circumferentially disposedcluster of permanent magnets and a continuous ring of nonmagneticmaterial generally surrounding and holding said magnets, a supportingring constructed of magnetic material and supporting said separate unitand providing a return magnetic path for said magnets, said supportingring being a pre-existing component usually serving a first function ina machine assembly other than a function as a portion of a generator andin such first function being adapted to be rotated.

2. In the dynamoelectric machine of claim 1 said separate unit beingsupported on said supporting ring with a snug -fit with said supportingring in engagement with one radial side of said magnets.

3. In the dynamoelectric machine of claim 2 said separate unit-having aplurality of magnet shoes in engagement with said magnets on the otherradial side of said magnets rwith said continuous ring holding saidmagnets and said shoes together.

4. In the dynamoelectric machine of claim 3 said shoes having bevelededges extending radially to diverge from the outer to the inner surfaceof said shoes, said continuous ring having one surface flush with theouter surfaces of said shoes and having another surface flush with theexposed face of said magnets, said continuous ring engaging said bevelededges.

5. In the dynamoelectric machine of claim 4 said continuous ring beingsubstantially wider in an axial direction than the width of said magnetsand said shoes.

6. In the dynamoelectric machine of claim 5 said magnets being curvedceramic magnets having convex and concave surfaces and with said shoeshaving convex and concave surfaces with said magnets and said shoeshaving convex and concave surfaces engaging each other.

7. In the dynamoelectric machine of claim 6 the radial thickness of saidcontinuous ring being no greater than the combined thickness of saidmagnets and said shoes.

8. In the dynamoelectric machine of claim 7 said supporting ring being aflywheel.

9. In the dynamoelectric machine of claim 7 said supporting ring being aring gear.

10. In the dynamoelectric machine of claim 7 said continuous ring beinga member cast about said magnets and said shoes.

References Cited UNITED STATES PATENTS 2,930,916 3/1960 Scanlon et al.310-156 3,072,813 1/1963 Reijnst et a1. 310-156 3,132,270 5/1964 Phelon310-156 3,237,034 2/1966 Krasnow 310-156 MILTON O. HIRSHFIELD, PrimaryExaminer.

L. L. SMITH, Assistant Examiner.

